Neutral grounding resistors

The neutral of the transformer or generator is connected to ground through a Neutral Grounding Resistor (NGR) to limit phase-to-ground fault currents.

Resistance grounding may be either of two classes, high resistance or low resistance, distinguished by the magnitude of ground-fault current permitted to flow.

Why limit the fault current

1. To reduce burning and melting effects in faulted electric equipment, such as switchgear, transformers, cables and machines.
2. To reduce mechanical stresses in circuits and apparatus.
3. To reduce electric-shock hazards to personnel.
4. To reduce the arc blast or flash hazard to personnel.
5. To reduce momentary line-voltage dips.
6. To secure control of transient overvoltages.